Clamp for master sheets of printing machines



Jan. 17, 1956 L. F. MITCHELL CLAMP FOR MASTER SHEETS OF PRINTING MACHINES 2 Sheets-Sheet 1 Original Filed Jan. 22, 1952 & M

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CLAMP FOR MASTER SHEETS OF PRINTING MACHINES Original Filed Jan. 22, 1952 2 Sheets-Sheet 2 25 2e 2 /5 INVENTOR.

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drmeuw United States Patent CLAMP FOR MASTER SHEETS OF PRINTING MACHINES Lester F. Mitchell, Shaker Heights, Ohio, assignor to Addressograph-Multigraph Corporation, Cleveland, Ohio, a corporation of Delaware Original application January 22, 1952, Serial No. 267,530. Divided and this application November 12, 1952, Serial 8 Claims. (Cl. fill-415.1)

This invention relates to improvements in or relating to a clamping device for securing one end of a printing plate or master sheet on the drum or cylinder of a rotary printing machine. The present application is a division of my prior application filed January 22, 1952, and assigned Serial No. 267,530, now abandoned.

The present inventionis particularly concerned with the provision of a clamping device which will facilitate rapid mounting of the leading end of a thin flexible printing plate on the drum without manipulation of the clamping device other than by its contact with the printing plate. Further, the invention is concerned with the provision of an improved clamping device which will accurately position and secure one end of a thin flexible printing plate to the periphery of a printing drum without damage to the plate, and in a manner which will permit the plate to be readily removed. These therefore are the general objects of the present invention.

A. further object of the present invention isto provide a device for clamping one end of 'a thin flexible printing plate, as for instance, a plate made of paper, on a printing drum without either damage to the plate or the use of springs.

According to the present invention there is provided a printing drum having an axially extending recess formed in its periphery in which an anvil and a plurality of master plate clamping magnets are mounted, the magnets being normally held in position by magnetic force so that they may move yieldingly to permit the end of the master plate to be inserted between them and the anvil, the magnetic force of the members thereafter being utilized to clamp the master plate between the members and the anvil consequent upon tensioning of the plate.

in the drawings, Fig. l is a fragmentary plan View of a printing machine having a printing drum equipped with the improved printing plate clamping mechanism;

Fig. 2 is a perspective view of a portion of the clamping mechanism removed from the printing cylinder;

Fig. 3 is a transverse section, as indicated by the lines 3-3 on Fig.1, and illustrates the printing drum and clamping mechanism in end elevation;

Fig. 4 is a sectional view, on an enlarged scale, illustrating the clamping mechanism as used to clamp 21 pair of super-imposed printing plates in position, the plane of the section being indicated by the line 4-4 on Fig. 1;

Fig. 5 is a sectional view similar to Fig. 4, but with the printing plates removed; and

Fig. 6 is a sectional detail, similar to Fig. 5 but taken in the plane indicated by the line 6-6 on Fig. 1.

Referring now to the drawings, particularly Figs. 1 and 2, it will be seen that the improved clamping device is illustrated as being mounted on a printing drum or cylinder carried by a shaft 16 which is suitably supported by and between a pair of spaced end plates or frame members 17. The drum may be rotated by any suitable driving mechanism, not shown, but which coacts with a gear 18, shown in Fig. 1 as being secured to one end of the drum. The drum 15 has an axially extending slot or recess '19 formed in its periphery, and in which the improved clamping device 20 is mounted.

The improved clamping device includes an elongated channel-like support 21 which is secured to the drum 15 within the recess 16 and which has an upwardly opening recess 22 extending longitudinally of the drum adjacent to but below the periphery thereof.

The inner face 25 of the leg 26 of the supporting channel 21 forms the anvil against which the leading end of the printing plate A is clamped by individually movable, spaced clamping magnets 30. Each magnet comprises a cylinder formed of a material which, when magnetized, has a high coercive force, such as Alnico." The magnets 30 are positioned in the channel 21 with their axes extending lengthwise. The channel is slightly wider than the diameter of the magnets 30 and is made of a nonmagnetic material. The magnets 30 are preferably longitudinally spaced one from the other by cylinders 31 having substantially the same diameter as the magnets 31 but which, like the channel 21, are made of a non-magnetic material.

The magnets 30 and spacing cylinders 31 are retained in the channel 21, and the magnets 30 are cammed into wedging contact with the anvil surface 26 by an elongated bar of magnetic material which, as shown, is secured to the upper end of the other leg 27 of the channel 21. This bar projects into the channel and restricts the width of its throat to a distance less than the diameter of the magnets 30 and spacing cylinders 31thereby retaining the magnets and cylinders in the channel 21. The bar 35 is spaced from the bottom wall 29 of the channel 21 to per mit vertical movement of the members 30 and 31. The inner face of the bar 35 is beveled to provide a cam surface 37 which cams the magnets 31 into wedging contact with the anvil surface 25 as they move upward in the channel due to their magnetic attraction to the bar 35.

The printing plate A is placed in the improved clamp by first introducing the leading or foremost end of the plate in the entrance angle or throat 38 which is formed by the surfaces of the clamping magnets 30 and the surtface 25 of the anvil or leg 26 of the channel 21. The plate is then shoved downward between the magnets and anvil until the end of the plate strikes the bottom wall 29 of the channel 21. As the master plate is moved downward, the magnets 30 roll downward along the cam surface 37 'of the bar 35. During the downward movement of the master sheet the magnetic attraction between the bar and the magnets 30 serves to yieldingly retain the magnets in the upper portion of the channel or groove 22 and in contact with the inclined cam surface 37 of the bar 35. When the plate A has been fully inserted it is tensioned by slowly drawing it outward which causes it to be wedged in place by the action of the cylindrical magnets 30 on the cam surface 37. The printing plate then may be held tensioned as hereinafter more fully described. However, it has been found that once tensioned,

the tension may be released without danger of being released from the clamp.

The printing plate may be removed from the clamp either by manual depression of the magnets 30 or by first moving it toward the bottom of the channel 21 and then quickly drawing it outward.

The scale of the clamping device has been greatly enlarged in the drawings, particularly in Figs. 3, 4 and 5. However, it has been found preferable to use magnets having a diameter of from three to six thirty seconds of an inch for the clamping members.

The opposite or trailing end of the printing plate may be secured to the drum by a suitable tensioning device. As indicated in Figs. 1 and 3 the drum 15 may be provided with a series of spaced slots 50 which extend into the wall of the drum adjacent the side of the drum recess 1.) which lies opposite the clamp 20. The trailing edge of the tensioned printing plate is drawn across such slots and is held against the surfaces 51 of the drum between the recessesfitl, by av series, of pins 52. .mounted in an axially extending ban 5.3. The;,ends ,of the .bar 53.-ar,e.

provided-with. extensions 54, cachet. which, is provided with a slotted opening 55..-(Fig..;.3),.v Theseopenings 55;

receive respective. pins 5.6whichiextend-axially from the oppositeends. of thedrum. Suitable springs 57rare'intenposed between the bar 53 andlhe drum. to retain. the barinpositionadjacent thedrumrsurface andatthe same time draw it. .inwardly, .s.o, that .the;p ins 52, which have. been forced through thetrailing end ,of the printing plate, will. draw. the plate tightly QCEO SaihQ drum. surface and.

maintain ,itv tensioned.

When itis; desiredv to remove theyplate from the drum... thetrailing end of, zthel-plateis releasedby. raising, .thebar; 53, frontfingagement with theplate. For; thispurpose the. operator grasps-a lip 58. ofgtheibar 53 and. moves: the: bar outward. against the actionofi the springs 57,,lthus freeing that end of. the; plate.

As heretofore mentionedit ispreferable that. a series...

of: individually movable, spaced magnets. be; used.

Accordingly, when the plate A has been clampeddotho.

drum, a narrowplateBmay bra-positioned to. overlie-portions of. the plate A- by insertingpne-end of the plate B-- between theplateA and; certainv of the magnets. 30. This may be. accomplished without disturbing the other clamp-- ing rnagnets,whichrnaintain the main plate. A in position. T his facilitates the use. of supplernental master; plates. to' supply. data in addition .to. that on. themain plate. Like wise, thesupplemental plate. may beblank so that itmay be usedto eliminate part of the data. .on. the .mainplate A. The supplemental. plate- B, is inserted andremoved in the same man-neras heretoforedescribedin connection with the main plate A. I

From the foregoing it will be s.een.that thepresent invention provides a simple andefiicientadevicefor clamp ing the leading end of a printingplate to .a printing drum which avoids the use of springs. Further the. movable members of the device are so positioned that; the-centrifugal forcedeveloped by the rotation of. the drum act-s. Furtherthearrangemerit of the clamp is, such; that a relatively small force to. increase. the. clamping action.

ter sheet 7 on theperiphery. of a printing 1 machine drum an; axially. extending, recess: formed in; its pcripheralpsurfiaee;

said devicecomprising ananvil formcdof-nommagllntie. material mounted'in the. recess, .ag sheet clamping member comprisinga permanent magnet mounted for movement to and from the anvil: to permit a sheet, to-beinserted. therebetwecn, and guidemeans-formed of: a: magnetioma;

terial to attract an,d tQ- guide said. magnet into.wedging engagement with a. sheet.positionedpn the anvil consequent upon tensioning of said sheet.

Further;

'2. A clamping device according to claim 1 having a pluralityof cylindrical magnets spaced in a row with their axes aligned and parallel with the axis of the drum.

3. A clamping device according to claim 2 wherein the guiding means comprises acommon cam bar formed or" a magnetic material which acts to cam the individual magnets into wedging contact with amastersheetpositioned between the magnets-and anvil.

4. A. clamping device. aecordingto. claim. 2,. wherein the magnets-arezaxially spacedby movable cylinders. made of non-magnetic material.

5. A clamping device for securing a. thin flexible master sheet on the periphery of; a printing-machine drum having an axially extending recess formed in its. peripheral surface, said device comprising an anvil mounted in the recess and maderofz'a-nonamagnetic'material, a plurality of sheet clamping magnets mounted for movement to and .fronathe anvilzto permit a. sheetto; beinserted therebetween, magnet-attractingmeans secured. to said anvil to; attract said; magnets, andguidemeans to. guide. said,

magnets into. wedging engagement,with. a. sheet positionedon the anvil consequent-upon movement of said magnets towards, said. means 6. A -cIampingsdeYice: aecording to claim 5, wherein the,..magl tetgcomprise=ag series voficylindrical membersv cxtendinge iallyi relativeto the. drum, and means including; a:,pl u-ra1ity of nonymagnetic cylinders. substantially aligned withthe magnets andinterposed alternately therewith to; spaee-the-magnetsaxially from each other.

7. Aclarnping deviceeaocording to claim 6, wherein the magnets;and nommagnetic, cylinders all have the same externaldiameten 8..A,clamp ing device for securing athin flexiblemaster-sheet :on a printing drum having an axially extending dividuallydnto wedging engagementwith the other leg of said. channel consequent upon movement of the magnets away frornthechannel, .anda barof magnetizable mate rial rigidly. Secured tojthe channelj and-to whichv the magnets areattraeted said; bar being positioned to cause themagnetic attraction to move the magnetin a direction out of the channel.

References.- Cited: in the. tile of this patent UNI-TED. STATES PATENTS 2,123,297" Jir'ousek July 19', 1938 2,213,014 Owen Aug. 27', 1940 2,231,291 Morrison Feb. 11, 194i 2,382,600 Bobst et' al Apr. 14; 1945 2,597,178, Pleydell et al.. l l May 20, i952 

